This invention relates to industrial baghouses and, more particularly, to method and apparatus for tensioning cylindrical filters bag.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emissions. One technique which has proven highly efficient in controlling air pollution has been the separation of undesirable particulate matter from a gas stream by fabric filtration.
Such filtration is carried out in dust collection apparatus known in the trade as a "baghouse" which operates on the same general principle as an ordinary household vacuum cleaner, except on a much larger scale. Basically, the baghouse is a sheet metal housing divided into two chambers, referred to as plenums, by a tube sheet. Disposed within openings in the tube sheet are fabric filters. A dust-laden gas stream induced by the action of a fan, blows into one chamber (dirty air plenum) wherein dust accumulates on the fabric filter as the gas passes through the fabric into the other chamber (clean air plenum) and out an exhaust.
Although all baghouses are designed in accordance with the foregoing general principles, there are numerous operational and structural distinctions. The present invention relates to a baghouse wherein a plurality of cylindrical filter sleeves having closed upper ends are vertically suspended in the clean air plenum from a bag support framework. The lower ends of the bags are fixed to openings in a tube sheet or cell plate. Filtration of the process gas occurs from inside to outside of the bags. As a result, baghouses constructed in this manner are normally referred to as inside-to-outside bag collectors.
During continuous operation of the baghouse, the bags must be periodically cleaned to remove the filter cake which accumulates within the cylindrical sleeve. This may be done by interrupting the flow of process gas carrying particulate matter and then causing reverse cleaning air to flow from the clean air plenum to the dirty air plenum. The reverse flow of cleaning air causes the dust cake to be dislodged and fall through the interior of the bag to the dirty air plenum for removal by an auger or similar means. In some baghouse installations, reverse air cleaning may also be supplemented with mechanical shaking of the filters.
The air cleaning process reverses the pressure drop the fabric filter normally experiences during filtering operation. In other words, the filter sleeve tends to collapse inwardly when being cleaned. This tendency is limited somewhat by circular support rings sewn to the outside of the bag at spaced intervals along its length.
Proper tensioning of the bags plays an important role in limiting fabric collapse during the cleaning process. If the bags are stretched too tightly between the supporting framework and the cell plate, the bags do not collapse during cleaning, but they tend to wear out quickly. If, on the other hand, the bags are installed too loosely, the fabric between adjacent skeletal support rings collapses during cleaning and will not permit the dust cake to fall through the bag to the bottom of the dirty air plenum.
Even when a bag filter is properly installed and tensioned correctly, it is reasonable to expect the fabric to stretch slightly with age and with repeated cyclings between filtering and cleaning. Thus, the bags must be periodically checked and the tension readjusted for each bag from time to time.
The installation and maintenance of filter bags of this genre has traditionally been a time consuming, costly and disagreeable task. Accordingly, there is a long felt need in this industry for improvements in filter bag assemblies and in techniques to alleviate the many installation and maintenance difficulties which have been encountered in the past. The primary goal of this invention is to meet this need.
More specifically, an object of this invention is to provide a method and apparatus for tensioning cylindrical bag filters to decrease installation and maintenance time and cost heretofore associated with baghouse operations. Also, the improved method and apparatus achieves the added advantage of prolonging bag life which, in turn, results in a less rigorous maintenance schedule.
Another object of the invention is to provide a method and apparatus for properly tensioning filter sleeves to permit controlled flexure of the bags during the cleaning cycle.
An additional object of the invention is to provide a method and apparatus for tensioning filter bags for quick and safe installation or maintenance by semi-skilled personnel. Installation and proper tensioning can be accomplished by one or two workmen who can achieve uniformly tensioned bags in minimal time. Thus, the method and equipment preserve high moral during bag installation or replacement which has traditionally been considered an unpleasant job in the hostile environment of a baghouse.
A further object of the invention is to provide a bag retainer assembly which may be easily and quickly removed whenever replacement of the filter becomes necessary.
Yet another object of the invention is to provide a self tensioning bag retainer which accommodates tne anticipated stretching of the filter bag over time and which adjustably maintains appropriate tension on the filter.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawing.